Transforming growth factor-β1 reduces megalin- and cubilin-mediated endocytosis of albumin in proximal-tubule-derived opossum kidney cells
Transforming growth factor-β1 reduces megalin- and cubilin-mediated endocytosis of albumin in proximal-tubule-derived opossum kidney cells
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DOI：
10.1113/jphysiol.2003.048074
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发表时间：
2003-10-15
影响因子：
5.5
通讯作者：
Christensen, EI
中科院分区：
文献类型：
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作者：
Gekle, M;Knaus, P;Christensen, EI
转化生长因子(TGF)- β(1)是一个多功能细胞因子超家族的成员，参与肾脏的多种病理过程，包括纤维化、细胞凋亡和上皮-间质转化。这些事件导致小管间质纤维化和肾小球硬化。对tgf - β(1)诱导的细胞功能改变知之甚少。近端小管细胞的一个重要功能是通过meggalin -cubilin依赖性受体介导的内吞作用对过滤蛋白（包括白蛋白）进行重吸收。在这项研究中，我们使用了一个建立良好的细胞培养模型（近端小管来源的负鼠肾（OK）细胞），以验证tgf - β(1)减少巨高泌素介导的内吞作用的假设。先前我们已经证明，在OK细胞中白蛋白的内吞作用是由巨高蛋白/立方蛋白介导的。tgf - β(1)导致meggalin -cubilin介导的内吞作用的时间和剂量依赖性下调，而不影响所测试的其他两种运输系统。配体白蛋白的结合、内化和细胞内运输受到影响。在200,000 g膜组分中cubilin和meggalin的表达减少导致结合减少。tgf - β(1)作用的潜在机制与丝裂原活化的蛋白激酶、蛋白激酶C或A或活性氧无关。相反，tgf - β(1)诱导的巨噬蛋白介导的内吞作用下调对翻译和转录的抑制很敏感，并且在此之前会发生Smad2和3的磷酸化。显性阴性Smad2/3结构阻止了tgf - β的作用(1)。总之，我们的数据表明，在各种肾病中发生的tgf - β(1)水平升高可导致巨噬甘肽依赖性内吞作用的下调。可能是tgf - β(1)导致受体介导的内吞作用负调节因子的Smad2-和smad3依赖性表达。
Transforming growth factor (TGF)-beta(1) is a member of a superfamily of multifunctional cytokines involved in several pathological processes of the kidney, including fibrogenesis, apoptosis and epithelial-mesenchymal transition. These events lead to tubulointerstitial fibrosis and glomerulosclerosis. Less is known about TGF-beta(1)-induced alterations of cell function. An important function of proximal tubular cells is reabsorption of filtered proteins, including albumin, via megalin-cubilin-dependent receptor-mediated endocytosis. In this study we used a well established cell culture model (proximal-tubule-derived opossum kidney (OK) cells) in order to test the hypothesis that TGF-beta(1) reduces megalin-cubilin-mediated endocytosis. Previously we have shown that albumin endocytosis in OK cells is mediated by megalin/cubulin. TGF-beta(1) led to a time- and dose-dependent downregulation of megalin-cubilin-mediated endocytosis without affecting two other transport systems tested. Binding, internalization and intracellular trafficking of the ligand albumin were affected. Decreased binding resulted from reduced cubilin and megalin expression in the 200 000 g membrane fraction. The underlying mechanism of TGF-beta(1) action does not involve mitogen-activated protein kinases, protein kinase C or A, or reactive oxygen species. In contrast, TGF-beta(1)-induced downregulation of megalin-cubilin-mediated endocytosis was sensitive to inhibition of translation and transcription and was preceded by Smad2 and 3 phosphorylation. Dominant negative Smad2/3 constructs prevented the effect of TGF-beta(1). In conclusion our data indicate that enhanced levels of TGF-beta(1), occurring in various nephropathies can lead to downregulation of megalin-cubilin-dependent endocytosis. Probably, TGF-beta(1), leads to Smad2- and Smad3-dependent expression of negative regulators of receptor-mediated endocytosis.